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effluent being produced ; but hitherto, I believe, no trials have
been made with London sewage, and whether it will prove
practically applicable, trial only can determine. Important points
to be ascertained are : The durability of the filtering material;
the cost of keeping the filters in order; and the proportion of
precipitating material necessary to be used.
The Webster Electrical process consists in passing the raw
sewage through a shoot in which are placed a series of iron plates,
about one inch apart, these being in electrical contact with the
dynamos. The working trials of this process were made at Crossness,
with a plant capable of treating 15,000 gallons per hour.
The electrical action produces hydrated ferrous oxide, which is not
only a deodorizer, but also possesses the property of removing
soluble organic matter; the resulting effluent, moreover, not being
liable to secondary putrefaction. In practice it was found that in
London sewage the whole of the matters in suspension were removed,
and from 50 to 60 per cent. of the oxidizable organic
matters in solution. It is estimated that a nett purification of
the whole of the crude seAvage to the extent of from 70 to 80 per cent. may be effected at a cost not exceeding £70,000 per annum
for coal and iron ; and it is alleged that when irrigation is used,
the process will render immense service as an efficient deodorizer,
and also materially enhance the rapidity of filtration. This process
is considered by Sir Henry Roscoe practicable, as regards the
London sewage, and as it appears to afford a reasonable prospect
of a solution of the question, pending the maturation of a scheme
for conveying the sewage to the land, a few details as to mode
and cost of operation will not be out of place. The necessary
plant consists of electrolytic channels, containing the iron plates ;
copper conductors and measuring instruments ; dynamos ; engines
and boilers. Iron is the best of all metals for the required purpose,
as sulphuretted hydrogen cannot exist where ferrous or ferric
oxides are present. Cast iron plates of the commonest quality,
moreover, employed as electrodes, give the best results. The
plates are set longitudinally in channels, through which the sewage